1. Field of the Invention
This invention relates to a device for the transmission and distribution of the vibration and stress exerted by a vibrator on objects such as stakes, tubes or sheet piles, with a view to driving them home, with a horizontal cross-section of dimensions exceeding those of the vibrator.
2. Description of the Prior Art
We know that the vibrators commonly used for this type of application are huge machines comprising at least one couple of offset rotary weights rotated in opposite directions and at a same speed by a motorization.
By way of these arrangements, the centrifugal forces generated by the rotation of the weights add up in a direction defining an axis of work. The centrifugal forces compensate one another in the other directions to cancel one another out in a direction perpendicular to the axis of work.
Usually, the vibrator is suspended at the end of the cable of a crane or similar mechanism, via a device (lifting eye) enabling the vibrator to be displaced vertically.
In the case of the cross-section of the object to be driven into the ground being greater than that of the vibrator, the transmission and distribution of the stress between the vibrator and the object to be driven into the ground are usually performed by a transmission and distribution chamber made of welded sheet steel which is fastened on one side, e.g. by bolting, to the underside of the vibrator (usually a fastening sole plate) and which bears, on the other side, a fastening device that can be adapted to the dimensions of the object to be driven into the ground. This chamber can, e.g., be constituted by two braced parallel plates by a partitioning forming crossbars as represented in U.S. Pat. No. 3,224,514.
When tubular stakes are involved, this device comprises a multiplex device, e.g. a so-called "quadriplex" device, made up of four rail sections or four "T"s bolted to the chambers and a hydraulic clamp mounted slidably with a locking facility on each of the sections or "T"s.
Experience has shown that, due to the intense stress to which it is subjected, the transmission and distribution chamber tends to deteriorate rapidly and must be frequently reloaded or replaced.
Detailed examination of the used chambers reveals that the deteriorations materialised in the form of cracks located along the welding seams and at the base of the protruding portions of the vibrodriver sole plate are due both to the quality of the chamber welding seams and to the heterogeneity in the mechanical behaviour of the chamber at the level of the welding seams. It so happens that this heterogeneity is particularly significant due to the distribution of the reverse bendings at the frequency of the vibrations generated by the vibrator.